Ceramic treating process and product produced thereby

ABSTRACT

A NEW CERAMIC TREATMENT PROCESS AND PRODUCT AND, MORE PARTICULARY, A PROCESS FOR TREATING UNDERFIRED POROUS PARTIALLY VITRIFIED RELATIVELY SOFT MACHINABLE REFRACTORY CERAMIC MATERIALS TO PRODUCE HARDENED DIMENSIONALLY STABLE END PRODUCTS AT RELATIVELY LOW TEMPERATURES AND THE CERMAMIC MATERIALS PRODUCED THEREBY WHICH ARE SUITABLE FOR APPLICATION AS BEARINGS FOR UNDERSEA SUBMERGENCE, LOW TEMPERATURE BEARINGS FOR ARCTIC VEHICULAR AND MACHINERY APPLICATIONS, PRECISION BEARINGS FOR SPACE USE AND LIQUID METAL LUBRICATE SYSTEMS. THE SOFT CERAMICS CAN BE MACHINED AND SHAPED IN THE SOFT STATE AND HARDENED BY THE PROCESS OF THIS INVENTION AT TEMPERATURES WELL BELOW NORMAL VITRIFICATION TEMPERATURES WITH VIRTUALLY NO CHANGE IN DIMENSIONS FROM THE MACHINED UNTREATED CERAMIC TO THE TREATED AND HARDENED END PRODUCT. OTHER PRODUCTS PRODUCED BY THE PROCESS OF THIS INVENTION PRODUCE ARTICLES HAVING A VERY DENSE SURFACE CAPABLE OF TAKING A HIGH POLISH AND OTHER PRODUCTS HAVE RESULTED IN AN ABRASIVE OR POLISHING STONE HAVING SUPERIOR QUALITIES TO THOSE OF THE ARKANSAS STONES IN RESPECT TO BOTH SPEED OF METAL REMOVAL AND DEGREE OF POLISHING OR SHARPENING. IN ADDITION, OCARSER OR FINER GRADES ARE OBTAINABLE COMPARED TO A SINGLE GRADE OF ARKANSAS STONE. OTHER PRODUCTS PRODUCED BY THIS PROCESS HAVE NEGATIVE TEMPERATURE COEFFICIENTS BECOMING VERY GOOD ELECTRICAL AND HEAT CONDUCTORS AT HIGH TEMPERATURES.

United States Patent 3,817,781 CERAMIC TREATING PROCESS AND PRODUCT PRODUCED THEREBY Peter K. Church, Cascade, and Oliver J. Knutson, Colorado Springs, Colo., assignors to Kaman Sciences Corporation, Colorado Springs, Colo.

No Drawing. Original application June 1, 1967, Ser. No. 642,704. Divided and this application Apr. 16, 1970, Ser. No. 33,120

Int. Cl. C04b 35/00 US. Cl. 117169 23 Claims ABSTRACT OF THE DISCLOSURE A new ceramic treatment process and product and, more particularly, a process for treating underfired porous partially vitrified relatively soft machinable refractory ceramic materials to produce hardened dimensionally stable end products at relatively low temperatures and the ceramic materials produced thereby which are suitable for application as bearings for undersea submergence, low temperature bearings for arctic vehicular and machinery applications, precision bearings for space use and liquid metal lubricated systems. The soft ceramics can be machined and shaped in the soft state and hardened by the process of this invention at temperatures well below normal vitrification temperatures with virtually no change in dimensions from the machined untreated ceramic to the treated and hardened end product. Other products produced by the process of this invention produce articles having a very dense surface capable of taking a high polish and other products have resulted in an abrasive or polishing stone having superior qualities to those of the Arkansas stones in respect to both speed of metal removal and degree of polishing or sharpening. In addition, coarser or finer grades are obtainable compared to a single grade of Arkansas stone. Other products produced by this process have negative temperature coefiicients be: coming very good electrical and heat conductors at high temperatures.

CROSS REFERENCE TO RELATED APPLICATIONS soft refractory ceramic comprises the steps of shaping an underfired partially vitrified relatively soft refractory ceramic into a predetermined shape, impregnating the shaped ceramic with phosphoric acid and curing the impregnated ceramic at temperatures of at least 600 F.,

but below vitrification temperatures for a time sutficient to drive out the moisture and produce a hard ceramic.

Ceramic materials normally undergo substantial dimensional changes during the usual firing or vitrification steps. Thus, it has heretofore been extremely diflicult to produce precision parts or intricate shapes from ceramics. Precision parts had to be shaped slightly oversize b efore firing. After firing, the ,parts required further machining with diamond cutting wheels or by using lapping methods.

Many intricate shapes were just not available since thin duce a. ceramic having all the characteristics of a vitrifiedv ceramic without the usual change in; dimensions. The process of the instant invention appears to be useful in the treatment of such refractory ceramic materials as the oxides of aluminum, beryllium, zirconium, titanium, magnesium and the like. These materials in the commercially available machinable grade are quite soft and easily broken. Also, in the soft state, they can be readily cut with carbide cutting tools, drilled, filed, sanded and otherwise formed to practically any desired shape. One such aluminum and beryllium oxide material is available from Coors Ceramic Company of Golden, Colorado. When the machinable ceramics are treated by the method of this invention, they become very hard, approximating highly vitrified ceramic and, in addition, will retain the original machined and pre-treated dimensions. The treated material becomes so hard that the only practical method to do further machining is with diamond cutting wheels or by using lapping techniques.

The commercial value of the instant invention is readily seen when it is recognized that close tolerances on many intricate vitrified ceramic parts can only be obtained by machining with diamond cutting methods after firing. This is the case since there is considerable shrinkage which occurs during the firing. Also, there are many desired shapes which cannot be economically cast or molded dur ing the firing process. In addition, it is often not feasible to construct molding dies for small quantities of a par-' ticular part. The method of the present invention in contrast thereto permits easy machining of parts to exact tolerances and then hardening the part without change in original dimensions.

It is, therefore, the principal object of this invention to provide an improved process for shaping, treating and hardening of machinable ceramics which avoids one or more of the disadvantages of prior art methods of producing close tolerance hardened shaped ceramic parts. i

A further object of the present invention is to provide an improved process of producing hardened ceramic articles of manufacture of predetermined shapes, of predetermined characteristics and of predetermined dimensions.

Another object is to provide an improved method of producing close tolerance ceramic shapes of selected hardness, porosity and surface, characteristics.

A still further object of the invention is to provide an improved process for the production of ceramic bearings capable of use with or without lubricants in hostile environments.

A further object of the invention is to provide an improved processfor the production of an improved abrasive or polishing stone.

A further object of the invention is to provide a process for the production of a refractory ceramic oxide material having a negative temperature coefiicient of electrical and heat conduction.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to thefollowing description, and its scope will be pointed out in the appended claims. 7 j

This invention is directed to a process and product involving a new type of ceramic material that is formed by chemically impregnating a relatively soft porous, underfired refractory oxide base material, followed by a low temperature cure. The resulting ceramic structure formed inthis manner has been shown to exhibit extreme hardness, a high compressive strength and a dimensionally stable material over a wide temperature range. In addition, a number of these new ceramic materials show an inherently small coeificient of friction coupled with a very low. wear. rate characteristic. 1 r

Parts can be economically fabricated of this new material in a wide variety of intricate shapes and sizes. This is most easily accomplished by machining the relatively soft and' porous refractory oxide base material to the final dimensions desired using conventional high speed steel or carbide tooling. The machined pieces are then chemically 3 treated and cured at a temperature substantially below that used for normal ceramic vitrification.

One of the unique features of this chemical treatment and hardening method is that virtually no change will occur in the original dimensions of the machined part during the hardening process. Therefore, expensive diamond machining of the finished hardened part is eliminated.

These new ceramic materials will withstand repeated water quenching from 1000 F. as well as prolonged exposure to temperature extremes of 2000 F. to -300 F. Mohs scale hardness is in excess of 9, normally being about equal to that of a silicon carbide. Rockwell hardness can be as high as A-85 to A-90, with associated compressive strengths in excess of 125,000 p.s.i.

In addition to their use for the manufacture of precision parts, many of these ceramics exhibit excellent characteristics for low friction and low wear rate bearing and seal applications; in particular, journal bearings, thrust bearings and sliding type bearings and seals. When used in this manner, lubrication may be by means of a wide variety of conventional and non-conventional lubricants. Among those successfully tested to date include: tap water, sea water, alcohol, kerosene, polyethylene glycol trichloroethylene, lubricating oils, silicone fluids and liquid metals. Solid lubricants have been used with good results at temperatures up to about 2000 F. In addition, lightly loaded bearings have been operated for limited periods at high speed without lubrication.

Life tests of sleeve-type bearings have been and still are currently in progress. However, to date wear has been too low to obtain quantitative data, even after many months time. Rub-shoe type wear rate tests have consequently been conducted and have shown exceptionally low wear rate characteristics. For example, a ceramic shoe of this invention riding on a ceramic wheel of the same material exhibited many times less wear than a bearing bronze shoe riding against a steel wheel using oil as the lubricating media. Also, unlike a conventional bronze-steel bearing combination, very heavy loads can be applied to many of the ceramic-to-ceramic material bearings without their showing any tendency toward galling, even when running with such poor lubricants as alcohol or water.

A special variation in treatment of this invention has also been found that will produce a honing or finishing material that appears to be superior in several respects 4 for example, one such ceramic will remove metal far more rapidly than will an Arkansas stone, while at the same time producing a finer and more highly polish finish. Another ceramic material of this invention displays a wide variation in electrical and heat conduction with relatively small changes in temperature.

The basic method employed for producing the new ceramic materials consists of chemically impregnating a porous, refractory oxide structure followed by a low temperature cure. The porous refractory acts as the skeletal framework around which the final ceramic structure is formed.

The simplest chemical hardening method consists of impregnating the porous refractory structure with a solution of phosphoric acid. The thoroughly impregnated material is then cured in an oven with the final temperature reaching at least 6001000 F., or higher. With a suitable refractory base material, this simple acid treatment will produce a hard ceramic body having numerous uses.

A more dense, harder and structurally stronger ceramic can be formed by impregnating the porous base material with one or more refractory oxides prior to the final acid treatment. This may be accomplished by impregnation of the porous structure with a water soluble metal salt solution and subsequently converting to the oxide by simply elevating the temperature to the required conversion point. Normally, this salt to oxide conversion will take place at a temperature less than about 1.000 F.

X-ray diffraction tests indicate that these chemical treatment methods form a new microcrystalline structure or at least a very close bond between the added oxides, and/or phosphoric acid and the porous refractory skeletal structure.

As mentioned previously, the ceramic material is built around a porous refractory base material that functions as the skeletal structure. The types of such materials that are suitable for use in the present invention include various grades of alumina, titania, beryllia magnesia, magnesium silicate and stabilized zirconia. Silica has been tested but does not provide satisfactory results. These materials were obtained from the manufacturer in an underfired or machinable form. In this condition, these materials were normally found to be soft enough to allow machining by conventional means, and exhibited a relatively high effective porosity (10% to to allow for subsequent chemical treatment by the process of this invention. Table I lists the major type designation, manufacturer, hardness, porosity and fabrication method for to both natural and artificially produced grinding stones. 50 each of the skeletal refractory materials tested.

TABLE I.UNDERFIRED POROUS REFRACTORY BASE MATERIALS Sintering Effective Mols, Manufacturer's temp., porosity, hard- Base material type designation Manufacturer Ma or oxide Other oxides F. percent ness Remarks 0.5% $103 Alumina AHP, 9Q Coors- 99% A120; 8.33 1(slag 2,670 45.7 2,3 Isostatlc, pressed.

o 8 99% A120: 2,3 Extruded. 99 Al 0; 0, 1 Do. 99% A1203 1 D0. 99 Al 0a Do. 99% A1203 5,6 D0. 99% A120; 4,5 08.51;.

- 99% A1203 D0. 99% A1103 D0.

.5% A1203 Extruded. 99.7% A1 03 -5 Cast.

0. Do AP,94, 11 d0 94% A; 0.75% MgO 1,700 33.1 2,3 Extruded.

0.5% ZrOz 0.1% F9203 3.75% S10 0.9% 0210 Do AP, 94, 12 ..d0 94% A: 0.75% MgO 2, 33.0 2,3 D0.

0.5% ZrOz 0.1% FezOa 3.75% S10: 0.9% 0220 Do AP,94,12 '.-...d0 94% A120: 0.7 MgO 2,130 44.1 2,3 Isostatic, pressed.

(Isostatie). 0.5 ZrOz TABLE IContinued Sintering Eflectlve Mols, Manufacturer's temp., porosity, hard- Base material type designation Manufacturer Ma or oxide Other oxides F. percent ness Remarks SiOz 2.75% MgO Alumina AP,85,11 Coors 85% A120: 1.25% 02.0 1,700 33.4 2,3 Extruded.

0 75% B210 0 F940; Do AlSiMag 614 Am. Lava C0rp-.... 96% A120: 2, 000 6,7 Too hard for easy (underfired). io machining. lSiMa 614. do 96% A120: M O 2 000 1,2 Ordered green, Do A (greeu Ca .O fired for 20 minutes at 2,000 F. Extruded rod. Do AlSiMag 393 do 90% A1203 4,5 Do- AlSiMag 548- "do..- 99% .8A1z03 Beryllia BP9611. Coors 96 B O 1,2 Extruded. Mamie i-=. 187E4 Du-GoCeram1es 89% MgO SrOZ 1,2 D0 -187E77. C 1l&%O g8 S102 M esium silicate "AlSiMa 222 Am. ava orp.... g 1 z 81 1 5; 3 porosiiy Amersil, Inc 99% S102 2,3 Hot pressed. Zirnnnia 1791120 Du-CoCer 95% ZrOz 5% 0210 1,2 Made from ZCA type F coarse grain zireonia- (CaO stabilized); SiOz L va Cor 98 TiOz MgO 2,000 2 3 Ordered Green Titania firiifiifir ga Am a p {CaO n r d gg l mutes Nora-American Lava Corp.-Chattanooga, Tenn; Amerisil, Ina-Hillside, New Jersey; Coors-Golden, Colorado; Du-Co Ceramlcs-Saxon burg, Penn.

These materials are fabricated by one or more of several commercially used methods such as powder pressing, extrusion, isostatic forming or slip casting. The important factor, however, is that formed or pressed oxide be only partially sintered since optimum sintering will result in a dense body with insufiicient porosity to be usable in the chemical treatment method of this invention.

In addition to the alumina, beryllia, magnesia, titania and zirconia materials, it is anticipated that many of the other partially sintered refractory oxides would make applicable skeletal structures for the improved ceramic material. Among these would be the oxides of barium, calcium, cerium, chromium, cobalt, gallium, hafnium, lauthanum, manganese, nickel, niobium, tantalum, thorium, tin, uranium, vanadium, ytrrium and zinc. Also, many of the complex-refractory oxides should be suitable base materials. Of the complex-refractories, only the magnesium silicate has been tested to date. Other complex-refractories that may be suitable if produced in a porous, partially sintered (under-fired) form are aluminum silicate, aluminum titanate, barium aluminate, barium silicate, barium zirconate, beryllium aluminate, beryllium silicate, beryllium titanate, beryllium zirconate, calcium chromite, calcium phosphate, calcium silicate, calcium titanate, calcium zirconate, cobalt aluminate, magnesium aluminate, magnesium chromite, magnesium ferrite, magnesium lanthanate, magnesium silicate, magnesium titanate, magnesium zirconate, magnesium zirconium silicate, nickel aluminate, potassium aluminum silicate, strontium aluminate, stronium phosphate, strontium zirconate, thorium zirconate, Zinc aluminate, zinc zirconium silicate and zirconium silicate.

The novel process according to the invention is particularly adapted to the treating of porous, partially vitrified refractory ceramics such as the oxides of aluminum, barium, beryllium, calcium, cerium, chromium, cobalt, gallium, hafnium, lanthanum, magnesium, manganese, nickel, niobium, tantalum, thorium, tin, titanium, uranium, vanadium, yttrium, zinc and zirconium and mixtures thereof. The oxides may be substantially pure or may contain or have small amounts of impurities or additives, such as an oxide of a metal other than that of the body such as copper, iron, chromium, manganese, nickel, titanium, magnesium, cobalt, cadmium and the like and/or other salts of such metals which ultimately will convert to oxides at least during the final curing step. The process of this invention also contemplates the addition of small amounts of additives such as a salt of a metal other than that of the body and convertible to an oxide such as the chlorides and nitrates of aluminum, copper, chromium, cobalt, magnesium, molybdenum, nickel, tin and zirconium which are added to the ceramic during treatment. It appears that the higher purity refractory ceramics are preferable where maximum hardness is desired.

The process of this invention comprises usually the forming of the untreated ceramic into a predetermined shape. It will be understood that, while precast machinable stock may be used, it is possible to precast to intricate shapes and prefire to an underfired condition before the ceramic is subjected to Applicants process. The machinable ceramic, either stock or custom cast, is usually quite porous. The simplest method of chemically hardening the porous, underfired refractory structure is with a single acid treatment. The ceramic is impregnated with a concentrated phosphoric acid solution, usually of concentration. The ceramic can be evacuated in a vacuum before immersion in the acid to hasten the impregnation or, as has been found to be particularly effective, the ceramic can be heated to from about 300 to about 600 F. and then immersed in the phosphoric acid solution. The heating causes a vacuum to be produced within the voids of the ceramic and the phosphoric acid will be drawn all through the ceramic upon immersion. While a considerably longer time is required, the ceramic also can be just immersed in the acid solution for a length of time suflicient for complete impregnation. Greater uniformity is achieved using the vacuum or heating impregnation techniques. When the part is thoroughly impregnated with acid, it is removed from the solution, excess acid on the surface is drained or wiped off.

Next, applicants novel process comprises the controlled heat curing of the acid impregnated ceramic. The heating cycle is usually started around F. and ends at about at least 900 F. The ceramic pieces are preferably placed in powdered asbestos, and the like, to minimize shock during the heating and cooling cycle. The powdered asbestos also serves to absorb moisture driven out of the ceramic as the temperature is raised. The temperature is raised during curing at a rate insufiicient to craze the surface of the ceramic.

As pointed out, one of the unique features of the method of the invention is that virtually no dimensional changes occur in the machined piece during the hardening process. Therefore, expensive diamond-type machining of a hardened part is eliminated.

The property of physical hardness has been used as the primary means of determining effects of varying the un derfired base materials, chemical treatment and curing 7 8 methods. Table II below sets forth the hardness measurehave been used with good success. It is found that, once ments for various materials which have been given a simple the heat treatment has been carried to above 850 F., the acid treatment. temperature may be increased to well above the normal TABLE II.HARDNESS MEASUREMENTS FOR SIMPLE ACID TREATMENT impreg- Mohs nation, hard- Rockwell Sample Base material Typo designation Manufacturer Ma or oxide percent ness hardness Remarks 21E Alumina AP-85-11 COOK'S 85% A120 (1 (1 94% A1203 94% A1203 94% A1203 99% A1203 99% A1203 Beryllia Magnesia do Du-Co Ceramics- Am. Lava Corp VI Amersil, Inc" (under-fired)- Am. Lava Corp..- T102 Du-Co Ceramics.- 95% ZlOz Am. Lava Corp-" MgO.SiO2

#3 porosity AlSiMag 192 C60 do. AP-99C-12 Coors 99% A1203 146 do AP-99C-L1 do 99% A120;

Several significant differences in the final product are vitrifying temperatures (e.g. 3000 F.) without producing achieved by the variation of portions of the treating procany shrinkage or change in the original physical dimeness. While a pure or nearly pure ceramic material can be sions. Further, the high temperatures do not appear to significantly hardened by a simple acid treatment, impregatfect the hardness of the material from that of the material nation of the ceramic with a solution of a salt convertible heated to 850 F.

to an oxide and converting same to the oxide will produce While the mechanism of applicants process is not an increase in the hardness of the ceramic and the further completely understood, it is believed that aluminum phosphate may be formed and deposited in the crystal lattice acid treatment produces an even harder end product.

structure of the aluminum oxide as well as within the Where the ceramic material is impregnated with 85% or higher concentration of phosphoric acid and heat ds of the porous ceramic. Further, the phosphates of treated, a good bearing material is produced and two the lmpurities and/or additives may be formed and pospieces of this same material will slide against one another srbly as part of the lattice structure.

with a low coefficient of friction. After such pieces are 3r As pointed out above, the ceramic materials which are worn in for a short while, a shiny surface film is produced Chemically treated and hardened according to one embodiwhich remains shiny even at elevated temperatures. Where me of the present process display the unique characteristhe more concentrated phosphoric acid is used, the resulttic of exhibiting a low coeflicient of friction when sliding ing product is more dense with smaller unfilled pores. against themselves. The coefiicient of friction between where a l i l Pure ceramic id i t t d, the identical pieces of the material is considerably less than addition thereto of another oxide during treatment subwhen used in contact with any dissimilar ceramic or metal stantially increases the hardness of the finished product. tested to date. While it is not completely known what occurs in the A t ough these materials may be operated dry where treating process, the pores of the underfired ceramic are they are lightly loaded for limited periods of time, the believed to be filled or partially filled with a reaction tarting friction is considerably higher than when a lubriproduct of the ceramic and the additive, if any, with the eating material is present. Lubrication may be by a number acid, probably a complex metal h h of different liquids such as tap water, sea water, kerosene, where the ceramic material i impregnated ith 85% trichlorethylene, lubricating oils, silicone fluids and liquid or higher concentration of phosphoric acid having dismetalsy lubricants Such as molybdenum (ii-Sulfide, l d therein l i Phosphate t l til t t d graphite and the like are also suitable. It is possible also at f 250 400 51 and i then hgat treated, a i l to form the lubricant in situ within the pore structure of is produced which cannot be polished to more than a dull the gfinish, is quite porous and makes an excellent polishing The hearings can be easily and e mically fabricated and sharpening stone. This characteristic is also produced in a wide variety of shapes and sizes. The untreated where the treatment with phosphoric acid is carried out 55 ceramic material in the form of partially fired bars or with dilute acid solutions. It is believed that less reaction plates is machined to size and shape using conventional product is available to fill the pores, providing a more high Speed steel or carbide tooling The machined pieces 85"; gggg gl li gz 55;}; 1 5 $323321? 1321; 28:8 8 are then chemically treated and hardened at temperatures g y substantlally below normal vitrification temperatures. The

hardness of the final prod The Starting Porous 31mm hardening occurs with substantially no change in dimennum oxide grades have ranged from about 25% to about o 60% effective porosity and, when sub ected to a starved g gi g g f' expenslve dlamond machmery of the acid treatment, remain quite porous which may account for the excellent polishing and sharpening characteristics of the thus treated material. as the lubricant reservoir analogous to that of sintered The heat treating of the acid impregnated ceramic bronze bearings. In other instances, the bearing can be Should be initiated at about 1500 F. to 3505 F. for a operated partially or totally submerged in the lubricant or Short period of time to drive out excess moisture and the non-rotating member can be connected to an external then the temperature is raised in steps for a series of time lubncant reservoirintervals until the final cure is accomplished at at least 7 yp hearings fabricated of ceramic according to the 500-600 F. and preferably at at least 850-900 F. present invention can Withstand repeated water quenching The ceramic bearing being fairly porous may be used The ceramic will become quite hard at 500 F.600 F., from at least 1000 as Well as Prolonged exposure to but good electrical resistivity is not achieved until the temperatures as high as 2000F and as low as 300 F. ceramic is subjected to a temperature of 850 F. or higher. The compressive strength is on the order of about 125,000

Temperatures above 1000 F. and as high as 3000 F. psi. or better, and the hardness on the Mohs scale is between 9-10 or on the order of about A-80 to A-90 on the Rockwell scale.

The ceramic materials of Table I were subjected to several slightly different treatments according to this invention, which are: (1) impregnation in phosphoric acid alone; (2) one or more oxide impregnations followed by a single phosphoric acid treatment; or, (3) one or more oxide impregnations alone.

A typical acid impregnation process according to the present invention comprises heating the ceramic piece to about 300-600 F. for about 20 minutes, the piece is then immersed in an 85% phosphoric acid solution while hot for about 40 minutes. The piece is then placed in an oven and progressively heated from 150 F. to about 1000 F. over a period of about 120 minutes. The piece is then cooled to room temperature.

A typical combination salt and acid impregnation process comprises heating the ceramic piece to about 250- 450 F. for about 20 minutes. The heated piece is then immersed in the salt solution for about 40 minutes. The piece is removed from the salt solution and cured progressively from 150 F. to 1000 F. over a period of 120 minutes. The previous step can be repeated if desired. The piece is then cooled to about 600 F. and immersed in an 85 phosphoric acid solution for about 40 minutes. The piece is then placed in an oven and cured over a temperature range of from 150 F. to 1000 F. over a period of about 120 minutes and subsequently cooled to ambient temperature in about 15 minutes.

Fully hardened samples were prepared according to the above treatments from the materials of Table I.

As previously stated, impurities existin in the base material appear to have an effect on the resultant hardness of the treated piece. Therefore, it was decided to artifically add refractory oxides to the porous base structure prior to treating with the acid. This was accomplished by impregnating the refractory base material with a nitrate, chloride, acetate or other highly water soluble salt of the oxide desired, and then converting the salt to the metal oxide by heating slowly to an elevated temperature. Following the oxide impregnation (which may consist of one or more salt treatment), the body was then treated with phosphoric acid in the same way as in the acid treatment alone.

Tables HI, IV, V and VI show the effect of added oxides to Coors alumina products AHP-99, AP-99-L3, AP-94- 11 and AP-SS-ll, respectively. In these tests, three impregnations of the saturated salts were used (to assure ample loading with the desired oxide), followed by the 85% phosphoric acid treatment.

It is interesting to note that these tables show a wide variation in hardness depending on the oxide treatment. In some cases, the hardness is considerably increased over that of the same base material treated with acid only, while in others, the increase is not so marked. The hardness that is obtained with the acid treatment only (no oxide impregnation) is listed for comparison purposes.

The CrO treatment is of special interest in that, when used with the 99%, 94% and A1 0 base structures, the resulting ceramic is exceptionally high in hardness as compared to all other oxide impregnations tested. These four tables also show that the AHP-99 material (99% A1 0 is the poorest choice for the base structure of these four types. However, since the AP-99-L3 is also a 99% alumina composition, it must be assumed that the hardness is not a factor of the refractory purity alone, but that other factors such as difference in effective pore size is probably responsible for some or all of the noted differences.

Tables VII, VIII and IX show the same type of data using aluminum oxides secured from the American Lava Corporation as their types 393, 548 and underfired 614. These are 99.8% and 96% A1 0 compositions, respectively.

Hardness measurements obtained with Coors 96% beryllium oxide for four different salt impregnations is shown in Table X. It is interesting that this base material produces results about equal to the best alumina material tested (Coors AP-99), indicating that refractory skeletal structures other than alumina are definite candidates for the ceramic fabrication method.

Tables XI and XII show hardness results for oxide impregnated magnesia material. While the hardness values are quite low as compared to the alumina or the beryllia, this is to be expected since magnesia, even in its fully fired state is not a particularly hard material (Mohs 5 /2 Tables XIII and XIV cover AlSiMag #222 magnesium silicate and Amersil 99% silica, respectively. For reasons not fully understood, refractory base materials containing a high percentage of silica do not appear to respond well to the chemical hardening method. Even in these two tests, however, the chromic oxide impregnation provided noticeably better results than the other impreg nations used.

Table XV lists results obtained with a partially sintered, zirconia refractory base material. This particular underfired zirconia was fabricated from a calcia stabilized but coarse grain material. It is anticipated that a fine grained zirconia, and possibly a magnesium oxide stabilized type, would provide better results. Nevertheless, the zirconia also reacts to the chemical hardening method in the same general manner as does the alumina, magnesia and beryllia, and, to a lesser extent, the magnesia silicate and silica materials. Table XV-A lists results obtained with aluminum oxide material and Table XVB lists results obtained with titanium dioxide material.

With regard to the effect of pore size, it would be noted that the AHP-99 Coors material has quite large pores, compared to the other Coors material, being on the order of less than one micron compared with 2 to 3 microns for the AI-I P-99 materials. It would appear that the pore size would preferably be less than 2 microns and substantially uniform in size.

TABLE IIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USING COORS AP-lM-l ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 8-9, Rockwell 70.7]

sP 4 impreg- Mohs Sample S No.salt nation, hard- Rockwell number Oxide formed impregnation impreg. percent ness hardness Cracks Remarks Al(NOa)2 3X 85 138012 3X 85 C0(NO3 3X 85 Cd(NOa)2 3X 85 9(N0s): 3X 85 C0(N0a)2 3X 85 CIO: 3X 85 C11(N03)g 3X 85 eGla 3X 85 La(N0a)2 3X 85 LiCzHaOz 3X 85 (CzHa 2)2 X 85 gCrO; X 85 NKNOa): 3X 85 311012 3X 85 SICNOa): 3X 85 TABLE III-Contlnued H3? 04 impreg- Mohs Sample Salt No. salt nation, hard- Rockwell number Oxide formed impregnation impreg. percent ness hardness Cracks Remarks 7-9 Th0: Th(NO3)4 3X 85 9-10 A-73.5 None- TiflCzOOa 3X 85 9-10 A-73.5 d0- 9-X H4SiW1eO4n 3X 85 9-10 A72.1 d0. Zn94 Z1101: 3X 85 8-9 A-73.8- -do 13- ZrO 01; 3x 85 9-10 A76.1 do

(1) FeCla I-A FezOa-CnOa lus 3X 85 9-10 A- --do (1 Cr0a TABLE IV.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-85-11 ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 8-0, Rockwell A-65.9]

HaPOl impreg- Mohs Oxide Salt N0. salt nation, hard- Rockwell Sample number formed impregnation imprcg. ness hardness Cracks Remarks AI(NO3)2 3X 85 8-9 A-71 None. Ce(NO3)z 3X 85 9-10 A-74 Yes-- r03 3X 85 9-10 A-81 None Mg(C2HaO2)z 3X 85 8-9 A-66 Yes Shattered during Rockwell test. Ti(C2O4)a 3X 85 8-9 A-68 Yes Do. ZrOCl2 3X 85 9-10 A-72 None TABLE V.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-99-L3 ALUMINA REFRACTORY BASE IWATERIAL [Acid treated hardness Mohs 8-9, Rockwell A-70.5]

HaPOl Salt No. impreg- Mohs Sample Oxide impregnasalt nation, hard- Rockwell number formed tion impreg. percent ness hardness Cracks Remarks CB(NO3)2 3X 85 8-9 A-69.1 Yes Explodedinoven. CrOa 3X 85 9-10 A-80.5 N0ne. MgCrO4 3X 85 9-10 A71.0 --do- ZrOClz 3X 85 9-10 A-60.1 do

TABLE VI.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNA'IIONS USING COORS AHP-QQ ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 5-6, Rockwell A54.8]

H3P04 No. salt impreg- Mohs Oxide Salt impregnation, hard- Rockwell Sample number formed impregnation nation percent ness hardness Cracks Remarks TABLE VIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 614 (UNDERFIRED) ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 8-9, Rockwell A-73.7]

HaPOA Salt Number impreg- Mohs impregsalt nation, hard- Rockwell nation impreg. percent ness hardness Cracks Remarks Ce(N0a)z 3X 85 8-9 A-69.0 N0ne.... Fractured during Rockwell test.

r03 3X 85 9-10 A-76.0 ..-do C0(N0a)2 3X 85 9-10 A73.0 do Do. MgCrOa 3X 85 9-10 A-65.5 do. Do. N1(NO3)2 3X 85 6-7 A-72.5 do Do. Zn(NO3)a 3X 85 6-7 A-73.3 do

ZrOGlz 3X 85 9-10 A-68.0 .do Do.

TABLE VIIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMP RE GNATIONS USIN G ALSIMAG 393 ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 8-9, Rockwell AN.M., i.e., not measured] HaP04 Salt lm- I lmpregna- Mohs Oxide pregna- No. salt tlon, perhard- Rockwell Sample number formed tion impreg. cent ness hardness Cracks Remarks A-4 CnOs CrO; 3X 85 9-10 A77.0 None MgCrzOa MgCrO| 3X 85 9-10 Shattered .do ZrO: ZIOCI: 3X 85 8-9 A68.5 do-.-

TABLE IX.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USING ALSIMAG 548 ALUMINA REFRACTORY BASE MATERIAL [Acid treated hardness Mchs 6-7, Rockwell A-N.M.]

HJPOI Salt imimpregna- Mohs Oxide pregna- No. salt tlon, perhard- Rockwell Sample number formed tion impreg. cent ness hardness Cracks Remarks A-l CraO: CrO: 3X 85 A M80130 MgCrOa 3X 85 A-3. ZrOz ZrOCh 3X 85 TABLE X.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS BP-QB-ll BERYLLIA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 6-7, Rockwell A-N. M.]

H3P04 Salt No. impregna- Mohs impregsalt tlon, hard- Rockwell nation impreg. percent ness hardness Cracks Remarks A1(N0s)s 3X 85 8-9 A-74 None CrO 3X 85 9-10] A-81 .d0 Shattered in Rockwell testing, MgCrO; 3x I 85 9-10 A-71 d ZrOClz 3X 85 9-10 A-75 D0.

TABLE XL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO 89% MAGNESIA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 4-5, Rockwell-Fractured] HsPO4 impreg- Mohs Oxide Salt im- N0. salt nation, hard- Rockwell Sample number iormed pregnation impreg. percent ness hardness Cracks Remarks Al(NOz): 3X

CrOz 3X z 2 4 8 base 61' t t d. ZrOU: 3X g D0. Sm egm e USING DU-CO 96% MAGNESIA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 4-5, Rockwell A-37.0]

HzP0| No. impregna- Mohs Salt salt tion, hard- Rockwell impregnation impreg. percent ness hardness Cracks Remarks TABLE XII.HARDNESS MEASUREMENTS FOR VAROUS OXIDE IMP RE GNATIONS TABLE XIIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USING ALSIMAG 222 MAGNESIUM-SILICATE REFRACTORY BASE MATERIAL [Acid treated hardness Mohs 2-3, Rockwell AN.M.]

s Oxide Salt im- No. salt nation, hard- Rockwell Samplenumber formed pregnation impreg. percent A1(N0a)2 3X 85 CID: 3X 85 MgCrO; 3X 85 ZrO 01: 3X 7 85 TABLE XIV.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING AMERSIL N0. 3 POROSITY SILICA REFRACTORY BASE MATERIAL [Acid treated hardness Mohs N.M., Rockwell A-N.M.]

v H3PO| v No. Impregna- Mohs Sam le Oxide Salt tion, hard- Rockwell num r formed impregnation impreg. percent ness hardness Cracks Remarks 0 1): 3X 85 4-5 None.-..

Ce(N0;)a 3X 85 4-5 ....-do 0 r0; 3X 85 WzHxOz): 3X 85 MgCrOr 3X 7 85 ZrOClg' 3X 85 TABLE XV. ISARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPgEGNATIONS I J I1;

ING DU-CO ZIRCONIA REFRACTORY BASE MATERIA [Acid treated hardness Mohs 8-9, Rockwell A-54.01

HaPOl No. lmpregna- Mohs Salt salt tion, hard- Rockwell impregnation impreg. percent ness hardness Cracks Remarks Al(NOa)a 3X 85 CrOa 3X 85 g( z a02)z 3X 85 MgCrOl 3X 85 Th(NOa)2 3X 85 znusom ax s5 Z!'0C l 3x 85 TABLE XV-A.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 614 96% A1 REFRACTORY BASE MATERIAL PARTIALLY SIN TERED AT 2,000 F.

(Acid treated hardness Mohs 8-9, Rockwell A-73.7I

HaPOl No. lmpregrla- Mohs Salt salt tion, hard- Rockwell 4 impregnation impreg. percent ness hardness Cracks Remarks CI'O: 3X 85 9-10 A-82.5 None ZrOCl 3X 85 9-10 A-74. do

MgCr04 3X 85 9-10 A-67.5 do

)(N a)2 3X 85 9-10 A-69.5 do

None 85 -6 A-655 do TABLE XVB.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 192 TITANIA 98% T: REFRACTORY BASE MATERIAL-PARTIALLY SINTERED AT 2,000 F.

[Acid treated hardness Mohs 4-5, Rockwell A-N.M.]

v HsPol N lmpregna- Mohs Salt salt tio hard- Rockwell impregnation impreg. percent ness hardness Cracks Remarks CrO; 3X 85 8-9 A77.5 None ZI'OCI: 3X 85 i A Be(NOa)z 3X 85 E( 2H:02)2 3X 85 1(N0a): 3X 85 MgCrO; 3X 85 Tables XVI-XXIX show the hardness of selected base materials which have been treated with multiple salt impregnations to illustrate the effect on hardness of varying the amount of added oxide prior to the final acid treatment. In the preceding Tables, all samples were impregnated with the salt solution three times. The following impregnations were varied from as few as one time to a maximum of eleven times. The base materials and oxide impregnations tested in this manner were selected from the materials of Table I.

Table XVI shows the effect of I through II chromic oxide impregnations using Coors AP-99-L3 alumina base material, while Table XVI-A shows the effect of 1 through 8 chromic oxide impregnations with AP-94-II alumina; base material'and Table xv-n shows 1' tbrbti' li'srmpreg nations with AP-94-l2 material.;These tables-show 1116 definite increase in hardness with increase in number of oxide impregnations. The rate or increase. inuhardnessmis also seen to decrease as the number of impregnations increase. This would appear to follow since there is probably less and less interstitial space for the oxides withleacli successive treatment. Specific gravity and porosity'te sts bear this out. 4 i

ENATIONS USING COORS AP-94-11 ALUMINA REFRACTORY BASE MATERIA a QA Salt impreg- Mohs Oxide lmpreg- No. salt nation, hard- Rockwell Sample No formed nation lmpreg. percent r -ness hardness Cracks-Remarks.

CrOa 1X 85 9-10 A-76.4 None.-.. CrOa 2X 85 9-10 A-80.7 .-.d CrOa 3X 85 9-10 A81.8 ...do CrO; 4X 85 9-10 CrOa 5X 85 9-10 A-S5.0 N0no.... CrOa 6X 85 9-10 A-85.0 ...do--.-- crol 7x as 9-10 A-86. 0-. ado.-." CIO: 8X .85

TABLE XVI.-HARDNESS VARIATION WITH NUMBER OF IcHRoMIo-ox'rpl: TMPREGNA- IIONS USING COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERlTA'L' 7. a r.,..M r Salt irnpreg- Mohs Oxide impreg- No. salt nation, hard- Rockwell Sample No. formed nation impreg. percent ness hardness Cracks Remarks CrOa 1X L 85 9-10 A1733 ..No CrOa 3X 85 9-10 A-A CrOa 5X 9-10 -A83.9 CrOa 7X 85 9-10 A-87.6 CrOa 9x 85 p 9-10 A-883 N0ne CrOa 11X 85 9-10 A-88.9

1 7 These tables show that there is very little difierence in the hardness results obtained between the AP-94-11 and the AP-94-l2 materials. The difference between these two base materials is in their sintering temperatures, respectively 1700 F.,'and 2130 F.

Table XVIII shows the results obtained with chromic oxide impregnations on Coors A'I-IP-99 alumina material. While the hardness increases with the number of chromic oxide impregnations, the hardness numbers obtained for a given number of treatments is much less than those obtained with chromic oxide treatment of Coors AP-99-L3 material of Table XVI. Since these alumina materials are both 99% aluminum oxide, and both have the same effective porosity of about 40%, the diiferences measured must be a result of the different pore size. The AHP-99 material has larger pores on the order of 23 microns average while the AP-99-L3 average pore size is 0.6-0.7 microns.

TABLE xvrL-HARDNEss' VARIATION WITH NUMBER OF OXIDE IMPREGNATIONS USING cooRs AP-94-12 ALUMINA REFRACTORY BASE MATERIAL HQPOI Salt lmpreg- Mohs Oxide impreg- No. salt nation, hard- Rockwell formed nation lmpreg. percent ness hardness Cracks Remarks Ir? CrzOa Cl'Oa 1X 85 9-10 A-75.8 Cl'zOa ClOa 2X 85 9-10 A-79.6 one, CrO; 3X 85 9-10 A8l.5 C170 CIO 4X 85 9-10 A83.9 01203 CrOs 5X 85 9-10 A-86.0 6X 85 CrzOa CrO: 7X 85 9-10 A-83.0 CI'zOa CrOa 9X 85 9-10 A84.0 Cr Og CrO; 11X 85 9-10 A85.0

TABLE XVIII.-HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNA- TIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL HzPOA Salt impreg- Mohs Oxide impreg- No.salt nation, hard- Rockwell Sample No. formed nation impreg. percent ness hardness Cracks Remarks Cl'Oa 85 85 8-9 A-57.4 None 85 9-10 A69.2 d0 85 8-9 A68.7 0..-. 85 9-10 A73.0 0

85 9-10 A80.0 None 85 9-10 A-76.0 None-..

TABLE XIX.-HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IMPREG- NATIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL HQPO! Salt impreg- Mohs Oxide impreg- No. salt nation, hard- Rockwell Sample No. formed nation lmpreg. percent ness hardness Cracks Remarks Y-l Z103 ZrOClg 1X 85 8-9 A-71.9 N011e-.. 85 8-9 A74.6 .d0 85 9-10 A-70.0 d0-- 85 9-10 A-73.0 None 85 9-10 A73.0 None.

85 9-10 A80.5 N0ne.---

ZIOCI: 85 9-10 A-78.0 None.

TABLE XX.HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IMPREG- NATIONS USING GOORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Salt, impreg- Mohs Oxide impreg- No.salt nation, hard- Rockwell Sample No. formed nation lmpreg. percent ness hardness Cracks Remarks ZrOOl 1X 85 5-6 A-55.5 None. ZrOClz 2X 85 9-10 A-63.5 d0.- ZrOCI: 3X 85 9-10 A61.7 do ZrOCl: 4X 85 910 A-71.6 -do...--

20 Tables XXI and DUI show similar tests to those just described except that the impregnant was magnesium chromate instead ofzirconyl chloride. 1 7

TABLE XXL-H'ARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IM- PRE GNATIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL H3PO4 Salt impreg- Mohs I I Oxide impreg- N o. salt nation, hard- Rockwell 7 Sample No. formed nation impreg. percent; -ness 7 hardness Cracks Remarks M-l MgCrzOi MgCrO4 1X 85 9-10 A-66 N one- M-2- MgCrzO4 MgCrO4 3X 85 9-10 A-72 do. M-3 MgCI204 MgCrO4 5X 85 9-10 A-70 d- TABLE XXII.HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IMPRE GNATIONS USING COORS AFP-99 ALUMINA REFRACTORY BASE MATERIAL H PO4 Salt Impreg- Mohs Oxide impreg- N0. salt nation, hard- Rockwell Sample No. formed nation impreg. percent ness hardness Cracks Remarks M-4 MgCnO4 MgCrOr 1X 85 6-7 A-50 None.-.

M-6 MgCrzO; MgCrO; X 85 9-10 A-Gl ..-do

1y. Again, the AP-94 material produces greater hardness Tables XXIII and XXIV are for ceric oxide impregthan the AHP-99 for comparable impregnations. Also, Rated and AHP99 base material, respectivelywhile the AP-94 material impregnated with zirconium oxide does not produce as hard an end product as does the chromic oxide impregnation, the reverse is true when considering the AHP-99 material. Again, the explanation is undoubtedly connected with differences in pore size and/ or impurities in the base material.

Table XXV covers the AP-94 material with cobalt nitrate used as the impregnant. Table XXVI is for the same base material but using a concentrated silico-tungstic acid solution for the impregnant. Table XXVII is again for the AP-94 base material but using a 1:1 mixture of ferric chloride and chromic acid as the impregnating solution to form a ferric chromite when cured.

TABLE XXIIL-HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNA- TIONS USING COORS AP-94-11 ALUMINA REFRACTORY BASE MATERIAL HaPO4 Salt impreg- Mohs Oxide impreg- No. salt nation, hard- Rockwell Sample No formed nation lmpreg. percent ness hardness Cracks Remarks Ce(NOa)z 2X (N0a)2 3X 85 C8(N0s)2 4X 85 Ce(NOa)z 5X 85 (N0a): 6X 85 TABLE XXIV.HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNA- TIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Salt impreg- Mohs Oxide impreg- N0. salt nation, hard- Rockwell Sample No formed nation lmpreg. percent ness hardness Cracks Remarks Ce(NOa)2 3X 85 8-9 A-54.9 None Ce(NOs)z 4X 85 8-9 A-59.4 .d0- Ce(NOa)a 5X 85 8-9 A59.0 do Ce(NOa)2 6X 85 8-9 A60.1 -.d0

TABLE XXV.HARDNESS VARIATION WITH NUMBER OF COBALT OXIDE IMPREGNA- TIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATER IAL HaPOl Salt impreg- Mohs Oxide impreg- Nov salt nation, hard- Rockwell Sample No formed nation impreg. percent ness hardness Cracks Remarks 00(N0a): 85 9-10 A71.5 N0ne.-.-

:32 "235""6-1'6"X ia'6" i-i6i1ial: 0001035? 5x as 9-10 A-74.5 None TABLE XXVI.-HARDNESS VARIATION WITH NUMBER OF TUNGSTIC OXIDE IMIIIREG- NATIONS USING CO ORS AP-94-12 ALUMINA REFRACTORY BASE MATERIA HaPO4 N0. impreg- Mohs Oxide Salt salt nation, hard- Rockwell Sample number formed impreg. impreg. percent ness hardness Cracks Remarks HiSiWitOm 1X 85 8-9 A-69.0 None H SiWuO-m 3X 85' 7-8 A71.0 H4SiW1sO4 4X 85 9-10 A-76.0 nlsiwlflolfl 5X 85 9-10 A-76.0

islwmom 6X 85 H4SiW1aO4o 7X 85 9-10 A-75.0

TABLE XXVH.HARDNESS VARIATION WITH NUMBER OF FERRIC CHROMITE IMPRE G- NATIONS USING COORS AP-94 l2 ALUMINA REFRACTORY BASE MATERIAL HaPO4 Salt No. impreg- Mohs Oxide impregsalt nation, hard- Rockwell Sample number formed nation impreg. percent ness hardness Cracks Remarks (1)F8Cla 4-A FeOzCXzOa 1X 85 6-7 A-72 None..-

(1)0r0a Z 2X (1)FeCla l-A FezOsClzOa 3X 85 9-10 A-75 None....

(1)0r0a (1)Fe01s 2-A rezoscrzoa 4X 85 9-10 A-77 do (1)Cr0s (1)FeCla 3-A FezOaCIzOa 5X 85 9-10 A-82 ..do

(1)Cr0s A zirconia base material has been used for tests shown as Tables XXVIII and XXIX. These are for a coarse grain,

calcia stabilized,

rial with chromic oxide and zirconium oxide impregnations as shown.

95% zirconia underfired refractory mate- 20 show that one phosphoric acid treatment is equal to, or

better than, more than one treatment.

TABLE XXVIIL-HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL H3PO4 Salt impreg- Mohs Oin'de impreg- No, salt nation, hard- Rockwell Sample number formed nation impreg. percent ness hardness Cracks Remarks 85 6-7 A69.5 None TABLE XXIX.HARDNESS VARIATION WITH NUMBER OF ZIRCONIUM OXIDE IMPRE GNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL H3PO4 Salt impreg- Mohs Oxide impreg- No. salt nation, hard- Rockwell Sample number formed nation impreg. percent ness hardness Cracks Remarks 23-Z ZIOz ZrOC12.. 3X 85 6-7 A-65 None ZrOC12 7X 85 6-7 Fractured 26-Z None None None-- 85 89 A-54 None TABLE XXX.MULTIPLE ACID IMPREGNATIONS USING COORS AP-94e-12 ALUMINA TABLE XXXL-MULTIPLE ACID IMPREGNATIONS USING COORS AP-85-11 ALUMINA REFRACTORY BASE MATERIAL Number H PO4 Number Salt salt impregacid Sample impregimpregnation, impreg- Mohs Rockwell number nation nation percent nation hardness hardness Cracks Remarks 85 1X 8-9 A61.2 Yes 85 2X 9-10 A-58.5 Yes..- Fractured; 85 3X 6-7 A-63.0 None 42% 1X 4-5 A 53.7 d0..... 42 5 2X 6-7 Fractured- Yes---" Fractured: 42% 3X 6-7 A67.6....- Yes--."

TABLE XXXH.-MULTIPLE ACID IMPREGNATIONS USING REFRACTORY BASE MATERIAL COORS AHP-QQ ALUMINA Number H3PO4 Number Salt salt impregacid Sample impregimpregnation, impreg- Mohs Rockwell number nation nation percent nation hardness hardness Cracks Remarks 85 1X 5-6 A44.2 None... 85 2X 6-7 A45.0 Yes Fractured. 85 3X 6-7 A68.0.-.- None..- 85 3X NM. NM. 85 4X NM. 85 5X NM. 85 6X NM. 42% 1X 4-5 42% 2X 6-7 Fractured. 42% 3X 6-7 A41.3 None--- now been found that this marked increase in hardness Table XXXIH shows the same type of multiple acid treatment test, except that the Coors (AP-94) material has been first impregnated with three chromic acid applications prior to the final acid treatments. Again, ment appears to be optimum.

one acid treat- TABLE XXXIII.-MULTIPLE ACID IMPREGNA'IION TEST USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL WITH CHROMIC OXIDE PIKE-TREATMENT Number HJPOI Number Salt salt impregacid Sample lmpreglmpregnation, impreg- Mohs Rockwell number nation nation percent nation hardness hardness Cracks Remarks CrO; 3X 85 1X 9-10 A-82.5 None--.

CrO; 3X 85 2X 9-10 A-8l.0 CrO; 3X 422/ 1X 9-10 A-78.1 CrO; 3X 42% 2X 9-10 A-8l.0 CrO; 3X 42% 3X 9-10 A-8l.0 do---- Tables XXXIV and XXXV show the effect of varying the phosphoric acid concentration. In the previous tests, the acid strength has been either 85% or 42V).% H PO In these two tests 95%, 90% and 75% phosphoric acid are Table XXXIV covers the AP-94 base material and Table XXXV the AHP-99 material.

fifth impregnant, silico-tungsten acid, has also been found to react in a similar manner.

Tables XXXVI and XXXVII respectively show the hardness measurements obtained with AP-94-II and also compared with the standard 85% strength treatment. 20 AHP-9'9 alumina base materials with multiple chrornic oxide impregnations only (no final acid treatment). Table XXXVIII covers the same two base refractory materials TABLE XXXIV.EFFECT ON HARDNESS F VARYING ACID CONCENTRATION USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Number HzPOi Number Salt salt impregacid Sample impregimpregnation, impreg- Mohs Rockwell number nation nation percent nation hardness hardness Cracks Remarks 95 1X 5-6 A-63.0 85 1X 6-7 A65.0 1x 6-7 A59.5 42% 1X 4-5 A-64.8 95 1X 9-10 A83.0 1X 9-10 A-80.5 75 1X 8-9 A-82.0 42% 1X 9-10 A-81.0 85 1X 9-10 A-81.5

TABLE XXXV.EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Number HgPO Number Salt salt lmpregacid Sample impregimpregnation, impreg- Mohs Rockwell number nation nation percent nation hardness hardness Cracks Remarks 1X 4-5 A46.0 None 95 1X 6-7 A56.0 d0 75 1X 6-7 A-46.0 .-..do 41% 1X 4-5 A-3l.7 do 95 1X 5-6 A-70.0 do 85 1X 4-5 A-74.0 .-..-do... 75 1X 4-5 A71.5 do

When conducting impregnation tests with various metal oxides, it was found that a marked increase in the Mohs 50 hardness scratch number occurred in several instances even before the final phosphoric acid treatment. It has TABLE XXXVL-HARDNESS MEASUREMENTS FOR MULTIPLE CD03 IMPREGNATIONS WITHOUT FIN BASE MATERI with multiple magnesium chromite impregnations only and Table XXXIX shows the same Coors AP-94-II alumina material, but using multiple ferric chromite impregnations. Table XXXIX-A shows the Coors AP-94-12 material with multiple tungstic oxide impregnations.

2% ACID TREATMENT USING COORS AP-94-12 ALUMINA REFRACTORY Salt 1131 04 Mohs Sample Base impreg- Not salt impregnahard- Rockwell number material nation impreg. tion ness hardness Cracks Remarks 0-1 AP-94-12 CrO; 1X None 4-5 A-430 None I ClOa 2X .....G 4-5 A62.2 do v CrOa 3X .-.--do- 8-9 A-74.0 do 01'03 4X .-d 9-10 A-82.0 .do f E CrO; 5X -d0-. 9-10 A-84.0 .do l v CI'O: 7X d 9-10 A-84.0 .do g j" CrOa 9X ..-.do 9-10 A-84.5 .do l CrOa 11X do 9-10 A-86.0 d0

TABLE XXXVII.-HARDNESS MEASUREMENTS FOR MULTIPLE CHO; IMPREGNATIONS ACID TREATMENT USING COORS AHP-99 ALUMINA REFRACTORY Salt H3P04 Mohs Sample Base impreg- No.salt impregnahard- Rockwell number material nation lmpreg. tion ness hardness Cracks Remarks CrO 1X None. 3-4 A15.2 None CrO 3X 6-7 A-54.7 do CrOa 5X 8-9 A69.0 ....-d0 OrOa 7X 9-10 A-75.0 do CrOz 9X 9-10 A78.0 do CrOa 11X 9-10 A79.5 do

TABLE XXXVIII.-HARDNESS MEASUREMENTS FOR MULTIPLE MAGNESIUM CHROMITE IMPRE GNATIONS WITHOUT FINAL ACID TREATMENT No salt H3PO Mohs Sample Base Saltimlmpregimpreg- Hard- Rockwell number material pregnation nation nation ness hardness Cracks Remarks M-l AP-94-12 MgCrO4 1X 4-5 A24.7 None. M2-- AP-9412 MgCrO4 3X 8-9 A 49.2 0 M-3 AP-94-12 MgCrO4 5X 9-10 A63.1 M-4.. AHP-QQ MgCr04 1X 3-4 A8.7 M5.. AHP-99 MgCr04 3X 6-7 A-28.8 M-fi AHP-BQ MgCrO; 5X 8-9 A39.0

TABLE XXXIX.HARDNESS MEASUREMENTS FOR MULTIPLE IMPREGNATIONS WITH- OUT FINAL ACID TREATMENT USING COORS AP-94-11 ALUMINA REFRACTORY BASE MATERIAL No salt H3PO4 Mohs Sample Oxide impregimpreghard- Rockwell number formed Salt impregnation nation nation ness hardness Cracks Remarks 4-A FezOaClzOa (1)F8C13+ (1)0103 1X 5-A FeOzCnOa (1)Fe 1a+(1)OrOa X 6-A FeaOaCnOa (1)FeC1;+(1)CrO; 5X

TABLE XXXIXA.HARDNESS MEASUREMENTS FOR MULTIPLE TUNGSTIC OXIDE IMPRE GNATIONS WITHO UT FINAL ACID TREATMENT USING COO RS AP-94-12 ALU'MINA REFRACTORY BASE MATERIAL N0. HBPOJ Mobs Base Salt lmsalt impreghard- Rockwell Sample No. material pregnatlon impreg. nation ness hardness Cracks Remarks H4SiW eO4a 1 X None H4SiWuO4o 3X .d0- H4SiWiuO4o 4X dO H4SiW1oO4o 5X --.-.d0 H4SiW1eO4o 6X d0 8-W AP-94-12 Hlsiwmolt 7X d0 Compressive strength tests have been conducted for several treated refractory ceramics using the ASTM tentative standard, Method C52-8-637.

The data presented in Tables XL, XLI, XLII, and XLIII cover Coors AP-94-1 l, AP-94-12, AP-85-11, AP99L3 alumina refractory base material, respectively, with a single acid treatment only.

and

TABLE XL.-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-11 ALUMINA REFACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY H@P04 Compreslmpreg- Sample sive Salt impreg- No.salt nation, diam- Area strength, nation impreg. percent eter (in?) Lb! p.s.i. Remarks Samplenumber:

1 None 85 .622 .303 22.7K 74,800 85 .623 .304 232K 76,500 85 .625 .306 242K 82,200 85 .622 .303 162K 53,500 85 .622 .303 22.4K 74,000

TABLE XLI.COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-12ALUMINA REFACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY HaPO4 Compresunpreg- Sample sive Salt impreg- No. salt nation, diam- Area strength, nation impreg. percent eter (in?) Lbt. p.s.i. Remarks Samplenumber:

1 None 85 .622 .303 263K 87,000 85 .623 .304 21.8K 71,800 85 .625 .306 25.7K 83,800 85 .621 .302 29.0K 94,000 85 .624 .305 22.0K 72,300

TABLE XLIL-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-85*11 ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Number HQPOJ Gomsalt impreg- Sample pressive Salt impregnation diam- Area strength,

impregnation nation percent eter (in?) L p.s.i. Remarks Sample number:

1 None 85 .625 .306 17.8K 58,300 2 do 85 625 306 20. OK 65, 500 3 do 85 .625 .306 126K 41,000 4 r10 85 .624 .305 12.7K 41,600 fin 85 .623 .304 18.95K 62,300

Avg 53,740

TABLE XLIII.-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP99L3 ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY H3P04 Compresimpreg- Sample sive Salt lmpreg- No. salt nation, diam- Area strength, 7 nation impreg. percent eter (in?) Lbl'. p.s.i. Remarks Sample number:

1 None 85 625 306 23. 6K 77, 400 2 do 85 624 305 21. 7K 71, 000 a do 85 625 305 21. 6K 70, 900 1 Aw 73,100

Tables XL'IV, XLV and XLVI cover Coors AHP-99 Modulus of Rupture tests have been conducted using the base material with three impregnations of chromic oxide, procedure of ASTM Method C369-56 with the exception magnesium chromite and zirconium oxide, respectively. A 15 that the sample size has been reduced. The ASTM Method final, single acid treatment was also used in each case. calls for samples in diameter x 6" in length. The

TABLE XLIV.COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPREGNATIONS PLUS SINGLE ACID TREATMENT HaPO4 Compresimpreg- Sample sive Salt impreg- No. salt nation, diam- Area strength, nation impreg. percent eter (inJ) Lbf. p.s.l. Remarks Sample number:

N-7 Cr03 3X 85 249 049 3, 900 78, 100 3X 85 250 049 4, 475 89, 600 3X 85 249 049 4, 150 85, 215 3X 85 250 049 3, 750 76, 375 3X 85 250 049 3, 050 62, 370 3X 85 249 049 4, 375 89, 835

TABLE XLV.-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING MAGNESIUM CHROMITE IMPREGNATIONS PLUS SINGLE ACID TREATMENT HaPOA Compresimpreg- Sample slve Salt impreg- No. salt nation, diam- Area strength,

nation impreg. percent eter (in?) Lbf. p.s.l. Remarks Sample number:

N-2 MgCrO; 3X 85 .250 .0492 4,175 83,600 N-3 MgCrO; 3X 85 .250 .0492 3,575 71,500

TABLE XLVI.COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-QQ ALUMINA REFRACTORY BASE MATERIAL USING ZIRCONIUM OXIDE IMPRE GNATIONS PLUS SINGLE ACID TREATMENT HaPOl C0mpres lmpreg- Sample sive Salt impreg- No. salt nation, diam- Area strength, nation impreg. percent eter (lnfi) Lbf. p.s.l. Remarks Sample number:

5. ZrOCla 3X 85 .249 .049 2, 375 47. 500 N-6. ZtOClz 3X 85 .250 .049 1,800 36,050

Table XLVII shows compressive strength measurements present ceramic samples have been prepared with dimenfor Coors AP-94-11 material with three chromic oxide sions on the order of A" in diameter x 2" in length. The impregnations, plus final acid treatment. sample size change was made because of the lack of curing ovens long enough to conveniently handle the 6" piece.

TABLE XLV1I.-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-11 ALUMINA REFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPRE GNATIONS HaIO4 Compresimpreg- Sample sive Salt lmpreg- N 0. salt nation, diam- Area strength, nation impreg. percent eter (111.2) Lbf. p.s.i. Remarks Samgle number:

5 CrO; 3X 85 .251 .049 6,100 123,730 C-6 CrOa 3X 85 .251 .049 6,600 133, 333

3,817,781 29 30 -Table XLVIIIslists the modulus of rupture test results AP-99-L3 base material with multiple (three and six) for the Coors AP-94-12 base material with multiple (zero, chromic oxide impregnations and with chromic acid plus three and six-)1 chromic.oxideimpregnations and Table other oxide impregnations. XLVHI -A 115141115 modulus of rupture tests for the Coors TABLE XLVIlL-MODULUS OF RUPTURE TEST DATA FOR COORS AP-94-12 (ISOSTATIC) ALUMINA REFRACTORY BASE MATERIAL H3PO No. impreg- Sample salt nation, Support Modulus number Salt impregnations impreg. percent Diameter distance Lbi. of rupture Remarks TABLE XLVIII-A.-MODULUS OF RUPTURE TEST DATA FOR COORS AP-QQ-L3 ALUMINA REFRACTORY BASE MATERIAL H3130! No. impreg- Support Sam salt nation, distance Modulus number Salt impregnations impreg. percent Diameter in. Lbf: of rupture Remarks 1 Nnnn s5 200 1. 50 82 17, 000

1a 0108 zr0o12-- 85 25s 1 50 14s as, 000

14 Cr0 ZIOCI2... 85 257 1 50 128 28,900

" '15. 010. Ni(NO )-2. 85 200 1 50 110 24,000

10---; 010. N1 N0.), 85 25s 1 50 124 27, 000

17 010. HASIWIGO4D-{% 85 .258 1.50 105 23, 400

10 010. Be(NO )2-. 05 .250 1.50 so 17, 800

Specific gravity determinations for a number of the porous refractory base materials, measured in the received condition, is presented in Table XLIX.

TABLE XLIX.-SPECIFIC GRAVITY DETERMINATION FOR VARIOUS REFRACTORY BASE MATERIALS WITHOUT OXIDE OR ACID TREATMENTS (AS RECEIVED CONDITION) Wt. in air I Salt No. salt H PO4 Volume (dry) Length Diameter Specific Sample number Base material impreg. p p s- (e (0 g av ty 0 AHP-gq None None 1. 684 3. 53 1. 471 1. 210 2. 10 393 5 AP-QQ-LS do rlo 1.674 3.95 1.474 1.205 2.36 on 41 -85-11 do do 1.045 0.04 1 450 1.200 2.39 4; -g4-11 do do 1 078 4.15 1 478 1.205 2.47

. p 12 do do 1 600 4.21 1.494 1.205 2. 40 E421 41 9442 (Tenemfiol do do 1. 678 3.60 1. 478 1. 204 2. 14

Specific gravity measurements for some of these same materials, but processed with a single phosphoric acid treatment, is listed in Table L.

TABLE L.SPECIFIC GRAVITY DETERMINATION FOR VARIOUS REFRACTORY BASE MATERIALS WITH SINGLE ACID TREATMENT ONLY Wt. in air Salt No. salt H5PO4 Volume (dry) Length Diameter Specific Sample number Base material impreg. impreg. impreg. (00.) (gms.) (cm.) (em) gravity A99 AHP-QQ Nnne 85 1. 71 4. 31 1. 494 1. 210 2. 52

.. 3. AP-99-L3 rin 85 1.678 4.63 1 474 1.206 2.75 A51 AP-85-11 do 85 1.632 4.49 1 466 1. 194 2.75 A41 AP-9441 do 85 1. 071 4. 74 1 475 1.204 2.83 2 AP-94-19 do 85 1.692 4.83 1.494 1 204 2.85

1 I A421 AP-04-12 (Isostatic) ..do 85 1.675 4. 32 1.478 1 203 2. 58

Table LI shows specific gravity measurements for Coors AP99-L3 alumina base material with 1 through 11 chromic oxide impre-gnations. This Table shows that a maximum density was obtained with six chromic oxide impregnations.

TABLE LI.SPECIFIC GRAVITY DETERMINATIONS FOR COORS AP-99-L3 ALUMINA RE- I FRACTORY BASE MATERIAL WITH MULTIPLE CHROMIO OXIDE IMPREGNATIONS H P01 Wt. in Air Sample Base Salt No. salt impreg., Volume (dry) Length Diameter Specific number matenal unpreg. lmpreg. percent (cc. (gms. (0111.) (cm. gravity "1---. AP'99L3 CrOa 1X None 1.337 3.70 704 1.555 2 77 2-. AP-99-L3 CrOa 3X 85 1. 349 4. 23 710 1. 555 3 09 3-- AP-QQ-LE! CrOa 5X 85 1.368 4.74 714 1.563 3 46 4.. 'AP99L3 CrOa 7X 85 1.337 4.95 .704 1.555 3 15.- AP-99-L3 CrOa 9X 85 1.391 5.30 6 1. 563 3 81 6 AP-99-L3 C1 03 11X 85 1. 334 5.07 .696 1.564 3 To determine the effective porosity of these ceramic materials, water absorption tests were made. The porosity percentage was calculated by determining the weight of the absorbed water in grams divided by the volume of the sample in cubic centimeters. This type of measurement gives the effective porosity only since there may be completely entrapped pores or pores too small to admit water.

Table LII shows the effective porosity measurements made for a number of the porous, underfired refractory base materials prior to any treatment of any kind. These materials show porosity variations ranging from about 30% to about 50% for the types tested.

the final phosphoric acid treatment. In this case, the samples measured approximately A" in the thickness by in diameter. Again, no cracking or structural failure occurred after ten cycles in either environment. Mohs hardness measurements also remained unchanged from the pre-test condition.

All the ceramic type materials produced according to the present invention have been repeatedly cycled between ambient temperature and 2000 F. This includes Coors AHP-99, AP-94, AP-85. to AP-99, basic alumina material with Cr O MgCr ZrO, and many other multiple oxide impregnations, as well as several similar combina- TABLE LII.-EFFECTIVE POROSITY DETERMINATIONS FOR VARIOUS REFRACTORY BASE MATERIALS WITHOUT OXIDE OR ACID TREATMENT (As received condition) Wt. Wt. in Salt HQPOA soaked air H Vol- Effective impreg- Numimpreg- H1O (dry) (gm.) ume porosity, nation ber nation (g.) (g.) absorbed (cc.) percent Tables LIII shows the same type data as above except 25 tions with the beryllia, zirconia and magnesia base mathat the porous base materials have been given a single phosphoric acid treatment only.

terials. It has also been found that ceramic parts produced by this invention can be cooled very rapidly after heating TABLE LIII.EFFECTIVE POROSITY DETERMINATIONS FOR VARIOUS REFRACTORY BASE MATERIALS WITH SINGLE ACID TREATMENT ONLY HaPO4 Wt. Wt. in

Salt impregsoaked air H10 Vol- Effective S an" pie Base impreg- Num nation, in H1O (dry) (g.) ume porosity, number material nation ber percent (g.) (g.) absorbed (00.) percent 99-... AHP-99 85 4. 64 4. 31 33 1. 710 19. 3 93.- AP-99-L3 85 4. 87 4. 62 25 1. 678 14. 9 51 AP-85-II 85 4. 70 4. 49 21 1. 632 12. 9 41.- AP-94-II 85 4. 95 4. 74 26 1. 671 12. 6 42 AP-94-12 -.-d0 85 5. 03 4. 83 1. 692 11. 8

421-. AP-94-12 1 do 85 4. 66 4. 32 28 1. 675 16. 7

* Isostatic.

Table LIV presents data obtained by using 1 through 11 40 to high temperatures. For example, a thin cross section chromic oxide impregnations followed by the single acid treatment. In this test, Coors AP-99-L3 base material was used. As in the case of the specific gravity measurements, minimum porosity occurs at about 9-11 impregnations.

piece can be removed from a 2000 F. oven and placed directly on an aluminum cooling plate without cracking.

Thin plates of Coors AHP-99 base material with single acid treatment have been exposed continuously to 1000 TABLE LIV.EFFECTIVE POROSITY DETERMINATIONS FOR COOKS AP99L3 ALUMINA REFRACTORY BASE MATERIAL WITH MULTIPLE CHROMIC OXIDE I21 IMPREGNATIONS aPO4 Wt. Wt. in

Salt impregsoaked air H10 Vol- Efiiective Sample Base impreg- Numnation, in H1O (dry) (gm.) mne porosity, number material nation ber percent (g.) (g.) absorbed (0.0.) percent 1 AP-99-L3 CrOa 1X None- 3. 95 3. 70 1.337 18. 2 2 AP-99-L3 CrO; 3X 4. 52 4.23 .29 1.349 21.5 W N 3 CrOz 5X 4. 95 4. 78 21 1. 368 15. 3 4 CrOa 7X 5. 10 4. 95 15 1. 337 11. 2 5 C103 9X 5. 32 5. 02 1. 391 1. 43 6 CrOa 11X 5. 08 5. 07 01 1. 334 0. 74 w Samples of AHP-99 alumina, with single acid treatment only, have been fabricated in the form of thin discs measuring A" x 3". They were then heated to 1000 F. and water quenched, reheated to 1000 F. and again quenched for a total of ten cycles. No visible signs of cracking or checking were observed.

The same type test has been performed with similarly prepared samples using liquid nitrogen as the quenching media. While liquid nitrogen does not produce as severe a thermal shock as does a good conductor such as water, sion. The samples were left immersed until gas formation it does, however, provide a much wider temperature excursion. The samples were left immersed until gas formation ceased and it is estimated that a temperature of about --300 F. had been reached. Again, no cracks or fatiguing were noticed after ten cycles.

These two thermal shock cyclings (1000 F. and liquid nitrogen) were repeated using AP-94-11 alumina base material. These samples were prepared, however, with three, five and seven chromic oxide impregnations prior to F. for 6 /2 days. No fracturing or cracking could be detected and the preand post-exposure hardness measurements were identical.

Additional samples were prepared using Coors AHP-99 and AP-94-12 base material with three magnesium chromite and five chromic oxide impregnations respectively. In each type sample, a final acid treatment was used following the oxide impregnation. These samples were exposed to 1000 F. for 60 hours followed by 8 hours at 2000 F. Again, no structural or hardness changes could be observed.

Sample ceramic parts (approximately 141" thick x in diameter) using AHP 99 base material with a single acid treatment have also been immersed in liquid nitrogen for 16 hours and then removed and returned to room temperature. No change in hardness was observed and no evidence of cracking or fractures could be found.

Tests have been conducted with machined rods and discs of ceramic materials produced by the instant process to determine what changes occur in dimension between the pre-hardened and the treated and hardened conditions. The accuracy of these measurements is considered to be 1:.0001 inches. 7

Table LV covers AP-99-L3, AP-85-11 and AP-94-l2 porous alumina machined pieces before and after a single acid treatment. These parts were cured at a final temperature of 1800 F.

TABLE LV.DIMENSIONAL CHANGE TE STS FOR HARDENED VS. MAX. TEMP. 1,800 E, 1 HR PRE-HARDENED CERAMIC MATERIAL,

Pre-hardened HaPO4 dimensions Hardened dimensions Percent change Sample Salt Numimpreg,

number Base material impreg. ber percent Length Diameter Length Diameter Length Diameter E AP99L3 None 85 4. 957 0. 3653 4. 955 0. 3652 -0. 040 --0. 027 C AP-94-12 do 85 0. 7001 O. 3781 0. 7001 0. 3779 -0. 058 B. AP-94 -11 do 85 0. 9467 0.8536 0.9457 0.8532 0. 105 0. 045 D AHP-99 CrO3 3X 85 0.8521 1 0940 0.8521 1. 0940 0 0 D4 518%.-. 3X 8; 0.1954 0 7560 0.1954 0.7555 0 -0. 066

4- 1 z X D 7 AILQHZ CIOLM 3X 85 0.8971 0. 3040 0. 8963 0. 3037 -0.0s9 0.096

NwvE.-Pre-hardened dimensions were read from the machined base material prior to any chemical treatment. Hardened dimensions were read after chemically treating part and curing to 1,800 F. for 1 hour.

Table LVI shows dimensional change readings for AP- 99-L3 and AP-94-l2 materials treated with multiple oxide impregnations followed by a final single acid treat ment and cured at a final temperature of 1800 F. Percentage values, as above, reflect change in dimension between those of the original machined basic porous structure and those obtained after the part has been chemically treated and hardened. As can be seen, the dimensional changes are exceedingly small.

TABLE LVI.-DIMENSIONAL CHANGE TESTS FOR HARDENED VS.

99 and AP94 alumina samples A and B do not display the X line, while samples C and D and the others treated with phosphoric acid according to this invention do provide the X line. The X line occurs at a d spacing of approximately 4.12 A. The nearest compound is that of AlPO aluminum ortho phosphate having the most intense line with a d spacing of 4.077 angstroms, relative intensity 100 in the 1-1-1 planes; next most intense line d spacing 2.506 angstroms, relative intensity 20, 2-2-0 planes; next most in- PRE-HARDENED CERAMIC MATERIAL MAX. TEMP. 2,300 F., 2 HRS Pre-hardened H PO dimensions Hardened dimensions Percent change Sample Salt Nmnimpreg, number Base material impreg. ber percent Length Diameter Length Diameter Length Diameter D70 AP99L3 ClOa 3X 85 1. 9765 0. 2570 1. 9765 0. 2570 0 0 AP99L3 Cr 3 6X 85 1. 9760 0. 2595 1. 9765 O. 2595 +0. 025 0 AP-99-L3 ZlOC12 5X 85 1.9760 0.2579 1.9765 0.2579 +0. 025 0 D73 AER-942126 C103 3X 85 1. 9824 0.2590 1.9815 0.2590 0.045 0 sos a AP-94-12 CrOz 6X 85 1. 9916 0. 2592 1. 9910 0. 2592 -0. 030 0 D7 A t i C 0 4X (isostatic). C12 2X 85 1.9805 0. 2681 1. 9300 0. 2681 -0. 025 0 NorE.Pre-hardened dimensions were read from the machined base material prior to any chemical treatment. Hardened dimensions were read after chemically treating part and curing to 1,800

Various of the treated ceramic materials have been subjected to a number of standard solvents and reagents. Little or no effect has been observed. Immersion tests for treated ceramics utilizing the single acid treatment only and for ceramic types incorporating various oxide impregnations, both with and without the final acid treatment, have been made in acetone, trichlorethylene, hydrochloric acid, sodium hydroxide, sea water, ferric chloride and concentrated sulfuric acid with no observable effect on either the hardness or physical appearance.

X-ray diffraction analysis of the structure of several types of treated ceramic materials has been conducted using a Norelco difiractometer manufactured by North American Philips, Inc. The results are briefly summarized in the following Table LVII. Accuracy of measurements can be considered to be at least 0.1%.

tense line d spacing 2.867 angstroms, relative intensity 10 1-1-2 planes; next line d spacing 3.162 angstroms, relative intensity 10, 02-1 and 2-0-1 planes. There are a number of lesser intense lines. It is important to note, however, that none of the lines with d spacing of 4.077 A.; 2.506 A.; 2.867 A.; 3.162 A. or any of the remaining lines appear on the X-ray diffraction chart of the aluminum oxide ceramic materials which have been treated with phosphoric acid according to the present invention. It is assumed that the phosphoric acid treatment results in or produces a new compound or at best a new crystalline structure which accounts for the improved and unique properties of the treated aluminum oxide materials. The source of informa tion for the X-ray data on aluminum ortho phosphate is the National Bureau of Standards Circular No. 5 39, Oct. 4, 1960.

TABLE LVII.X-RAY DIFFRACTION CRYSTAL STRUCTURE IDENTIFICATION B31304 Base Salt Numimpreg, material impreg ber percent X-ray ditfraction identification Sample number:

A None A1203 None A1103 A1203 X 85 A1203 X 85 Alto; Sl- ZlzPzO7 X (ZrOz,

race F AHP-99 MgCrO4 3X 85 Altzoa MgCr04 X -l- (C1203,

race MgCrOr 3X None A MgCrO4 CF03 3X None A1203 01103 0103 3X 85 A1203 01203 X 0103 3X None A1203 CrOa CIO3 1X 85 A1203 CIO: X Cl03 2X 85 A1203 0103 X C1O3 3X 85 A1203 C103 X 0103 4X 85 A1203 CIOa X OrO 5X 85 A1203 CrOs X CrOa 8X 85 A1203 Cl'Oa X Samples of ceramic material formed using Coors AP- 99-L3 alumina base refractory material with single acid treatment only (no oxide impregnation) have been subjected to various nuclear radiation environment.

One such test consisted of exposing small coil forms made of the material to a transient nuclear environment in a fast burst reactor. In this case, the small pieces A diameterx 4;" length) were exposed to a neutron flux rate of 2.8 10 n./cm. -sec. with associated gammas of 6X10 rads/sec. The total dose per burst was -2.2 10 n./cm. (fast nuetron), 1.8 10 n./cm. (thermal neutrons) and 10 rads. No noticeable effect in the ceramic material could be detected.

Another test was conducted in which small samples of the same type ceramic were irradiated for a period of time long enough to accumulate a total exposure of approximately (zmem). Even with this very high exposure, no physical change in the ceramic part could be detected.

Parts to be fabricated using the method and materials of this invention are first machined to the correct dimensions from the relatively soft, partially sintered, porous refractory base material.

In this original, untreated condition, the material will normally have a :Mohs hardness somewhere between 1 to 3 and preferably between 2-3 (such as the Coors AHP-99 and AP-'94 alumina).

This hardness range allows machining using ordinary high speed steel or carbide tool bits, drills, cutters, saws, etc. While carbide tooling is recommended for quantity production to reduce tool wear, high speed tool steel will also hold up quite well providing cutting speeds are low to prevent heat buildup at point of contact.

Very fine and intricate parts can be machined and processed from this material. Thin walled parts, such as coil bobbins, can be made with sections as thin as .010 with little difiiculty. Also, providing slow speeds are used to prevent heating, holes as small as have been drilled to an inch or so in depth.

*Recommended lathe turning speeds for small parts (l.4"2 dia.) are about 250 rpm. and drilling should ordinarily be done at speeds of less than 150 rpm. Band saw cutting should be at 10 ft./min. or less. Finished parts may also be easily sanded by hand using conventional wet or dri type silicon carbide paper with grit size ranging from 100 to 600, depending on the final finish desired.

Since the part will become extremely hard following the chemical treatment and hardening process, the dimensions and surface finish desired in the final cured state should be completed during the initial machinery operation. It is possible to provide final polishing operations after not more than three oxide impregnations using silicon carbide paper. After this point, it will usually be necessary to resort to diamond machining since the hardness of most of the hardened ceramic materials will usually exceed that of silicon carbide.

In order to fabricate a hardened ceramic part according to this invention, the piece, machined from the soft, base refractory material, must next be chemically treated and cured.

The chemical treatment method will normally consist of one of the following: (1) Impregnation in phosphoric acid only; (2) one or more oxide impregnations followed by a single phosphoric acid treatment; (3) one or more oxide impregnations without final acid treatment. The choice of impregnation method will, of course, depend on the final physical, chemical and electrical properties desired, as well as the economic factors involved.

Following each chemical impregnation, the part is elevated in temperature to remove the water (including water of crystallization) and to convert the salt, or acid solution to an inert crystalline structure. A typical impregnation and curing cycle is shown in Table LVIII.

TABLE LVIII.-CURING AND HARDENING CYCLE FOR UNDERFIRED REFRACTO RY CERAMICS Tempera- Time,

ture, min- Step Description F. ute

Heat basic ceramic materiaL. 350 20 2- Immerse part in salt solution 40 3. Cure part 150-1,000

4.-. Cool piece to 600 F 600 20 5. Immerse in phosphoric acid solution 40 6 Harden part -1, 000 120 7 0001 piece to ambient 15 1 Ambient.

The above applies to any part having its thinnest section not exceeding For thicker pieces, longer curing cycles (steps 3 and 6) and immersion times (steps 2 and 5) are required. Steps 2 and 3 may be repeated for desired number of salt impregnations, depending on mechanical strength properties desired. Where only acid treatment is desired, steps 2, 3 and 4 can be omitted. In like manner, if only an oxide treatment is to be used, steps 5 and 6 can be omitted.

Many of the refractory ceramic materials of this invention have been found to exhibit excellent characteristics for hearing and seal applications. Even the simple acid treated refractory base materials exhibit a noticeably low coefiicient of friction characteristic, suggesting possible bearing use.

Static and sliding coefficient of friction data has been measured for several refractory ceramic materials produced in accordance with the present invention.

Table LIX lists static coetficients determined by sliding various oxide impregnated specimens on a chromic oxide impregnated slide. The slide and most of the oxide impregnated sliders were also given a final phosphoric acid treatment. As can be seen from the data presented in Table LIX, the lowest coeflicient is provided by the like materials. The one sample, given four chromic oxide impregnations followed by one zirconium oxide impregnation (plus final acid treatment), produced the highest friction coefiicient when sliding against the chromic oxide treated slide.

Table LIX shows that the lowest friction coefiicients are generally obtained by sliding identical ceramic materials against each other rather than unlike materials.

TABLE LIX.--COEFFICIENT OF STATIC FRICTION MEASURMEN'IS, RUN DRY Slider Slide H3PO4 H3PO4 Friction Base Salt Numimpreg., Base Salt Numimpreg., Load coeflimaterial impreg. ber percent material impreg. ber percent Obs.) Lbf. cient AP-94-12--- OrO; 5X None AP-94-12 CrOa 4X 85 62.38 8.2 .131 AP9412 CIOa 5X 85 AP-94-12 CrOa 4X 85 62.38 11.4 .183 .AP-94-12-.. ZrOCo2 5X 85 AP-9112 CrOs 4X 85 62.38 9.6 .154 AP-94-12-.- MgCr04 5X None AP-9 1-12 CrOa 4X 85 62.38 9.8 .157 AP9412 Ni(NOa)a--- 5X 85 AP-94-12 CrOa 4X 85 62.38 8.8 .141 AP-94-12-.. CO(NO3)2 5X 85 AP-94-12 CrOs 4X 85 62.38 8.3 .133 AP94-12 SnCh.-. 5X 85 AP-94-12 CrO; 4X 85 62. 38 9.3 .149 AP9412 bore 1...: 85 AP-94-12 C1703 4X 85 62.38 10.7 .172

I a. X AP9412. plus 85 .AP-94-12 CrOa 4X 85 62.38 11.3 .181

ZrOCh 1X Norn.-Contact area of slider-=6 in.

Table LX lists coefficients of friction for some common materials and is included for comparison purposes.

TABLE LX.-COEFFICIENT F STATIC AND SLIDING FRICTION COMPRESSION DATA Static Sliding friction, friction,

Materials dry dry Glass on glass 0. 94 0. 4 Hard steel on hard steel 0.78 0. 42 Hard steel on graphite 0. 21 Hard steel on babbit 0. 70 0.33 Brass on mild steel- 0. 51 0. 44 Cast iron on cast iron 1. 10 0. 15 Teflon on teflon 0. 04 0. 04 Teflon on steel 0. 04 0. 04 Tungsten carbide on tungsten carbide 0.2 Tungsten carbide on steel 0.

lggomrutbove data from American Institute of Physics Handbook,

Wear rate test data was obtained with a variety of treated refractory ceramics using a single rub-shoe type test. Both conventional and non-conventional lubricants have been used in these wear rate tests, including SAE motor oil, glycerine, #200 polyethylene glycol,

attached. The wheel is directly driven by means of an electric motor. The slow drive speed has been used because wear rates are generally more severe at slow speeds than at high speeds since more surface-to-surface contact can occur through the lubricating film.

Since the shoe has a fiat contacting surface, the live contact pressure between shoe and wheel is extremely high at the beginning of the test. As would be expected, therefore, the highest wear is experienced at the start of the test with the wear rate diminishing with time (as the shoe wears, the p.s.i. loading decreases). While this type arrangement is unlike any actual bearing design, it does allow a convenient and rapid means of comparing wear rates.

Table LXI lists the types of treated refractory ceramic materials tested using the rub-shoe arrangement. For the most part, the variations consist in the oxide impregnation employed, which has been found to be a significant factor in the wear properties. Unless otherwise specified, the shoe Width has been standardized at 0.25" with a wheel diameter of 1.10".

TABLE LXL-RUB-SHOE TEST PARTS Final Roek- Mohs,

Base 1st Num- 2d Numimpreg, well hard- Part number material imprcg. ber impreg. ber percent hardness ness Remarks W-l AP-94-12 CrOa 5X CrOa 5X CIO3 4X None ZrOCl2 5X MgCrO4-.-. 5X Ni(NO3)z-.- 5X 00(NO5)2 5X SnClz 5X CrOa 8X MgCrOs 5X G.E.F.- Versilube silicone lubricant, alcohol, gasoline, paraffin, aprizon high vacuum grease, tap water and sea water.

The rub-shoe test arrangement consists of a single shoe riding against the periphery of a rotating wheel. The wheel in these tests have normally been operated at either or 300 rpm. The contact pressure between the shoe and wheel is variable and may be adjusted simply by changing Tables LXII through LXVI show comparison runs for various treated refractory ceramic materials using a variety of lubricants. Some comparisons have also been made with conventional bearing materials such as a bearing bronze shoe riding against a mild steel wheel. Such comparisons, however, are not too meaningful since the metal bearings are used only under very lightly loaded conditions with good lubricants or else galling occurs. The better treated refractory ceramic materials under these Weights on the end of a lever arm to which the shoe is 45 conditions show negligible wear.

TABLE LXII.-RUB-SHOE WEAR-RATE COMPARISON TESTS [Load, 10 lbs.; Run time, 1 hr. Lubricant, alcohol; R.p.m., 300; Wheel diameter, 1.1 Shoe width, .25; Base material, AP-94-l2] Wear H3P04 B31 04 Wear Wear Wear rate Wheel Salt Numimpreg, Shoe Salt Numimpreg., depth length Corrected width (in/ft.) number impreg. ber percent number impreg. ber percent (in.) (in.) depth (in) (in.) X10 Remarks CrO; 5X None W1 CrOa 5X None .000345 .240 .00033 .030 8rOz I 5X 85 W-Z 8183.4 ZX 85 .00029 .235 .00027 .030 53 r03 4X r a X ZIOCIT 85 W 3 ZTOCIT 35 .00010 .250 .00010 .025 20 None 85 W-5 None 85 000885 250 00089 060 175 ZrOC12-- 5X 85 W-6 ZrOC12. 5X 85 .00075 .250 .00075 .060 147 MgCrOr..- 5X None W-7 MgCrOr.-. 5X None .000485 .250 .00049 .045 96 N1(NO3)2. 5X 85 W-8 Ni(NOs)2- 5X 85 .000465 .250 .0004? .050 92 C0(NOs)2- 5X 85 W-9 Co(NOs)2- 5X 85 .00125 .250 00103 .075 200 511012... 85 W-10 S11 X 85 .00055 .250 00055 .050 107 CID: 8X 85 W-l-A CIO: 8X 85 .00000 N.M. 00000 NM. 0

TABLE LXIIL-RUB-SHOE WEAR-RATE COMPARISON TESTS [Load, 10 lbs.; Run time, 2 hrs.; Lubricant, alcohol; R.p.m., 300; Wheel diameter, 1.1; Shoe width, .25; Base material. AP-04-l2] Wear HQPO; H3PO4 Wear Wear Wear rate Wheel Salt N impreg, Shoe Salt Numimpreg depth length Corrected width GIL/ft.) number impreg. her percent number impreg. ber percent (in) (in.) depth (in.) (in.) X10- Remarks W-l CrOa 5X None W-l CrOs 5X None .00050 .235 .00047 .045 46 8IOa+ 2x 85 w-2 3 x 85 .00041 .220 .00035 .035 35 W-3 r a X a X ZroC12 {1X s5 w-a Zroclg 85 .000315 .220 .00028 .035 2a w-2 0:03 5x 85 W-9 Co(NOa)2. 5x 85 .0093 .245 .00001 .055 as 000103); 5x 85 W-2 CrOs 5x 85 .0071 .250 .00071 .000 5160 a s5 W-2 CID; 5x .0025 .230 .00024 .030 24 CrO s5 w-e CrOa-l- 4X 3 zroch 85 .0031 .200 .00025 .040 25 we 00 4x W3 00 ii i l' 3 1' 3 W ee ZIOCIT Zrooh 85 .00001 .220 .00021 .055 21 g l i h d O S e W1-A c103 8X 85 W-l-A Ct'Oa 8X 85 .000045 .215 .00004 .020 4 We Ni(NO.-1)z 5x 85 W-8 N1(N0a)z 5x 85 .000755 .245 .00015 .005 74 TABLE LXIV.RUB-SHOE WEAR-RATE COMPARISON TESTS [Load, lbs.; Run time, 1 hr.; Lubricant, H2O; R.p.m., 300; Wheel diameter, 1.1; Shoe width, .25 Base material, AP-94-d2] Wear HaPOi HaPO4 Wear Wear Wear rate Wheel Salt Numimpreg., Shoe Salt Numimpreg., depth length Corrected width (in/ft.) number impreg. ber percent Number impreg. her percent (in.) (in.) depth (in.) (in.) XlO-n Remarks $::13A---- ($83.4 85 W-l-A-. 983 1 8 X 85 N.M. N.M. N.M. N.M. N.M. High wear.

..... l 3 1' a X ZIOCIL s5 w-a Zroch 85 .000135 .190 .000103 025 W-2 CrOa 5X 85 W-2 CrOz 5X 85 .000145 .245 000142 .035 28 5 None 85 W-5 None 85 N.M. N.M. N.M. N.M. N.M. High wear. W-fi ZIOClz 5X 85 W-6 ZrOC12 5X 85 N.M. N.M. N.M. N.M. N.M. squeaks. W7 MgCIO4." 5X None W-7 MgOrOr.-- 5X None 00094 250 000940 070 177 W-8 Ni(NO3)2 5X 85 W-8 Ni(NOa)2 5X 85 N.M. N.M. N.M. N.M. N.M. Squeeks.

85 W-9 Co(NOa)2- 5X 85 N.M. N.M. N.M. N.M. N.M. Do. 85 W-10 Such--- 5X 85 00286 230 000263 115 52 85 W-Z-A CrOs 5X 85+ 000055 .225 .000050 .020 10 A1120; AlPOi TABLE LXV.LUBRICANT COMPARISON RUNS USING W-8 RUB-SHOE [NiO =5Ximpregnation] Wear Run Wear Wear Corrected Wear rat Load time depth length depth width (inJft Run number Lubricant (1bs.) (hrs.) Rpm (in.) (in.) (in.) (in.) 10- Remarks 1 Alcohol 2 300 .000765 .245 .065 74 30 2 300 000405 250 000248 050 24 30 2 300 N.M. N.M. N.M. N.M. N.M. 30 2 300 000005 175 010 5 Paraffin 30 2 300 TABLE LXVL-LUBRICANT COMPARISON RUNS USING W-3 RUB-SHOE [CrO =8X impregnation] Wear Run Wear Wear Corrected Wear rate Load time depth length depth width in. /it.) Run number Lubricant (lbs) (hrs.) Rpm. (in) (in.) (in.) (in.) X10 Remarks The treated refractory ceramic material has been found to perform most satisfactorily as a hearing when used against a like material. This is unlike metal bearings where different metals are invariably used to achieve low wear rates. The reason for this behavior is not fully understood.

The Bearings and Seals branch of the Marine Engineering Laboratory of the US. Navy Department employs a single rub-shoe test for their sea water lubricated materials. In this case, the shoe has a 1" width (usually made as a 1" cube) and rides on a 1%." wide x 2" diameter wheel. The r.p.m. is adjustable over a range of from 3 to 300. The standard loading is 4 lbs.

Similar tests were conducted using several of the single oxide impregnated chemically treated and hardened ceramic materials. Wear rates were measured to be between 1.55 10- and 31.1)(10 inches of wear/ft. of travel with 1" contact length, 4 lbs. load at point of contact, 60 r.p.m. wheel speed, sea water lubrication and 92 hours running time. This is at least two orders of magnitude less wear than with the titanium carbide/carbon combination presently being used for submarine seals by the M.E.L. Multi-oxide impregnated materials provide even lower wear rates.

Life tests have been made on several bearing configurations. They have been lubricated with various oils and water. Two oil lubricated bearings have a total running time to date of over 6615 hours at 1800 r.p.m. Without any visible signs of Wear. A radially loaded dual bearing had one bearing running in #10 SAE motor oil and the other running under sea water operated at 3200 r.p.m. The load on these hearings totals 1.5 pounds. These bearings have been operated continuously for over 5272 hours with no sign of wear. It should be noted that a bearing to be used with or under water should be cured at a temperature which is at least sufiiciently high to drive all of the water of crystallization out of the ceramic and convert the structure thereof to a water-insoluble state. As indicated previously, this temperature is found to be at least about 600 F. to about 1000 F. for the aluminum oxide ceramics.

It will be appreciated that these bearings have marine applications in a submersible system and would not require special seals, special lubrication or added buoyancy problems. Silicone lubricated bearings would be useful in low temperature applications and the bearings are also useful in liquid metal lubricated systems.

From room temperature to 600 F., the coeflicient of the treated refractory ceramic materials has been found to remain extremely low. The ceramic materials exhibit a higher friction coefficient between about 800 F. and 1200 F. Above this temperature, however, it again begins to slide more freely, attaining a reasonable low coeflicient as 2000 F. temperatures are approached. Since this behavior of increasing and then decreasing friction with temperature is almost identical to that reported for fully vitrified aluminum oxide ceramics, it is expected that the aluminum oxide base of the treated refractory ceramic is the major contributing factor to the related elevated temperature behavior.

The fact that the treated refractory material can be fabricated with a relatively high degree of porosity suggests the possible use of solid lubricants. This can be accomplished by impregnating the porous ceramic with a salt solution convertible to a solid lubricant, such as a salt of molybdenum or cadmium, and converting same in situ to the sulfide.

A variation in the chemical hardening and salt impregnation method of this invention results in an excellent abrasive material for the honing and finishing of metals. When treated correctly, such an abrasive stone will remove metal very rapidly in addition to having the feature of not loading the stone with metal particles.

The basic material found to be most satisfactory for this purpose is Coors AHP-99 aluminum oxide, although others have been found to be satisfactory. The chemical hardening treatment is different than that used to process standard treated ceramic parts and bearings, however. 

